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The Myth of Nitrogen Fertilization for Soil Carbon Sequestration

Department of Natural Resources and Environmental Sciences, Turner Hall, 1102 S. Goodwin Ave., Univ. of Illinois, Urbana, IL 61801. This study was performed with partial funding under Project 875397, Illinois Agric. Exp. Stn., and with support generated through the ¹⁵N Analysis Service

View larger version (40K): [in this window] [in a new window]   Fig. 1. Map of the Morrow Plots. U, unamended; U-NPK, unamended until 1955, currently fertilized for corn with 224 kg N ha–1, Bray-1 P = 56 kg ha–1, and exchangeable K = 336 kg ha–1; H-NPK, treated with manure, limestone, and rock phosphate from 1904–1966 and subsequently fertilized for corn with 336 kg N ha–1, Bray-1 P = 112 kg ha–1, and exchangeable K = 560 kg ha–1; M-NPK, treated with manure, limestone, and rock phosphate from 1904–1954 and since fertilized as with the U-NPK treatment; M, manured. The subplots studied are shaded.

View larger version (20K): [in this window] [in a new window]   Fig. 2. A century of changes in organic C concentrations for the plow layer in Morrow Plots cropped to continuous corn [C-C], a corn–oats (1876–1966) or corn–soybean (since 1967) rotation [C-O(S)], or a corn–oats–alfalfa hay rotation [C-O-H]. Open circles represent NB subplots with fertilizer and aboveground residue inputs beginning in 1955. Solid circles represent SA subplots with manure, limestone, and rock phosphate inputs before 1967, subsequently replaced by high NPK fertilization and aboveground residue return. Shaded boxes indicate the introduction of NPK fertilization. Triplicate analyses for organic C were performed by the method of Mebius (1960). Using the Tukey-Kramer statistic at = 0.05, significant differences must exceed 2.5 g kg–1 within a time series and 2.9 g kg–1 for comparison of individual values within a chart.

View larger version (14K): [in this window] [in a new window]   Fig. 3. Illinois data for fertilizer N input (open square) (Brown, 1955–1963; Illinois Department of Agriculture, 1964–2005) and grain N removal (solid circle) in corn, wheat, oats, barley, and rye (Secale cereale L.), calculated as a 5-yr moving average. Grain N removal was estimated using on-line data (USDA, 2007) for hectares harvested and mean yield (Mg ha–1), and grain N concentration calculated from textbook values for crude protein (Martin et al., 1976), assuming 175 (wheat) or 160 (all other crops) g N kg–1 protein.